1. Field of the Invention
The present invention relates to an abnormality detecting method for a form measuring mechanism and a form measuring mechanism using various probes such as a scanning probe, a touch signal probe, a probe for a surface roughness measuring machine, a probe for an contour measuring machine, etc., and more specifically, to an abnormality detecting method for a form measuring mechanism which is preferably used in a form measuring mechanism that measures changes of a measured object by bringing a probe into direct contact with the object to be measured, and makes it possible to easily judge contamination and wearing when the contamination and wearing occur on the probe and properly clean or replace the probe, and the form measuring mechanism.
2. Description of the Related Art
In a measuring mechanism which measures a form of an object to be measured, during repetition of measurements of the objects, the tip end of a contact type probe (hereinafter, simply referred to as a probe,) is gradually contaminated by several-micrometer to 0.1 millimeter orders of dust and oil on the object. Then, the contact sensitivity changes or foreign bodies such as dust are caught between the probe tip end and an object, resulting in a measurement abnormality. To avoid this, objects and the probe are soaked in a cleaning liquid and cleaned. However, only soaking in a cleaning liquid cannot sufficiently remove contamination, and removed contamination may adhere again, so that as shown in Japanese Laid-Open Patent Publication No. 2000-35325 (Patent document 1), it has been proposed that air is blown to the probe tip end to clean it as appropriate.
Further, the tip end of the probe is worn and deformed through use. Therefore, to enable accurate measurement even if the tip end of the probe is deformed due to wearing, as shown in Japanese Laid-Open Patent Publication No. 2001-280947 (Patent document 2), it has been proposed that a reference sphere for calibrating the probe form is provided and the probe is calibrated.
However, as shown in FIG. 13(a), assuming that measurement is made by using the reference sphere 30 shown in Patent document 2 in a state that dust 2, etc., adheres to the reference sphere 30 and/or probe 24, a form measured in this case is not the form that should be measured as shown in FIG. 13(b) but is the form measured in actuality as shown in FIG. 13(c). Therefore, from only the result of FIG. 13(c), it cannot be judged whether the measurement abnormality was caused by contamination on the tip end of the probe 24 or contamination on the reference sphere 30. Therefore, this requires extra labor of randomly repeating cleaning and measurement of the tip end of the probe 24 and the reference sphere 30.
Even when the contamination can be judged as contamination on the reference sphere 30 or the tip end of the probe 24, if the location thereof is not sufficiently identified, cleaning must still be repeated a plurality of times.
Further, when the probe 24 is used over a long period of time, even if it is calibrated by using the reference sphere 30, desired measurement accuracy cannot be secured when the probe is extremely worn out, so that the probe 24 needs to be replaced. However, due to influence from the contamination, it is difficult to judge whether the probe 24 has been worn out, and the time of replacement of the probe 24 cannot be judged.